Trypanosoma cruzi causes a chronic debilitating infection in many mammals, and in man causes Chagas Disease. The parasite infects 10-20 million people, and ten percent develop significant chronic pathology. The mechanisms involved in this process are poorly understood. The mammalian-stage of T. cruzi (CL strain) produces a family of 85-kD putative sialidases which are released from the parasite surface. The characterization of these sialidases, and how they may affect the host immune response are the long term goals of this project. Several genes encoding these sialidases have been cloned. The functional expression of these genes in eukaryotic expression systems is a specific goal of this project. The expression will permit analysis of individual sialidase requirements and substrate specificities. The effect that live parasites, crude preparations of secreted sialidases, and the recombinant expressed sialidases have on cells of the immune response will be investigated. Specifically, the effect on cell surface sialic acids of granulocytes, monocytes, macrophages, lymphocytes, and high endothelial venules will be studied. Fluorescent analysis with lectins specific for sialic acids, and monoclonal antibodies specific for sialic acids of an adhesion ligand (sialyl-Lewis-x) will be used to monitor the sialidase effects. The functional effects caused by the sialidases will be detected using in vitro cell adherence assays, and T-lymphocyte proliferation assays. Finally, studies investigating the mechanisms controlling the release of the sialidases from the surface will be initiated. Structural analysis of the sialidase anchor to the parasite will be performed.